import kotlin.reflect.KClass

class Thing<T: Any>(val key: T, val c: KClass<T>, neighbours: () -> List<Thing<*>>) {}

val a = Thing(1, Int::class, { listOf(b, c) })
val b = Thing(1, Int::class, { listOf(a, c) })
val c = Thing("hello", String::class, { listOf(a, b) })